Fiber reinforced boat hulls are common in the industry. Typically, they are made by a molding process that involves depositing (laying up) a layer of fibers, either as chopped fibers or a woven or knit mat of fibers, in a mold and then impregnating the fiber layer(s) with a resin which upon curing will provide water impermeability to the fiber and rigidity. Typically, such a boat hull is made in several steps of fiber deposition and curing steps, particularly when the boat hull has internal features such as a working deck, live wells, water collection sumps and other molding formed features. Often, the elements forming each feature of the boat are produced in a separate molding step which then requires a separate curing step. Also, such boat hulls typically have a finish coat on the exterior surface that contacts the water to provide both aesthetic appeal and a smooth finish. Such finishes may be in the form of a gel coat. Also, it is common to provide flotation chambers formed in the boat hull which are sealed from the outside atmosphere and may be filled with a flotation material such as a closed cell foam. Boat hulls of this type and their method of manufacture are well known in the art.
However, the method of manufacturing of such boat hulls is time consuming and complex. Additionally, the boat hull has many formed seams between the various components of the finished boat hull. For example, a seam is formed between the outside edge of the working deck and the main portion of the boat hull. These seams may be formed by joining the two components together during a secondary molding step or forming the parts separately and adhesively joining them together. In any event, such process is inherently inefficient because of the multiple steps of assembly and/or molding involved and curing between assembly steps. Additionally, the seams at the joints between the various components each provide an opportunity for leakage or lack of structural integrity.
Typically, the boat hull manufacturing process involves the use of at least one mold half and sometimes two mold halves for closed molding, the female mold half or sometimes referred to as the A mold and the male mold half, sometimes referred to as the B mold. When the hull forming assembly steps are performed sequentially, e.g., forming a hull and then forming a deck in the hull, additional and different mold parts may be required to effect the total assembly further increasing inefficiency and cost.
The production of fiber reinforced composite components, and in particular those components formed of a fiber/resin combination, have traditionally been accomplished by a number of open and closed molding lamination processes, or variations of each. Examples of these components include those used in the boating industry; such as fiber reinforced plastic sheets and parts with a compound shape used to manufacture a hull for a watercraft. These molding processes all involve a fiber reinforcement (e.g., fiberglass pieces) being laid up against a mold (e.g., a female mold) that provides the desired shape for the component, and the impregnation of the fiber with resin or a similar material. After curing, the resin/fiber combination forms a finished part that can be removed from the mold. Apart from these similarities, however, molding processes are distinct in the efficiencies provided by each, as well as in the disadvantages or tradeoffs encountered when choosing a molding process for fabricating a specific type or run of a component.
Vacuum bag molding is a type of closed molding technique that involves forming a thin flexible bag to cover the mold half upon which the fiber lay-up is positioned. The edges of the bag are then clamped, taped or otherwise secured to the mold to form a sealed envelope surrounding the fiber layup. One or more vacuum supply lines are usually installed within the bag to apply a vacuum on the bag interior concomitant with catalyzed liquid plastic or resin being introduced into the bag through a resin supply line to impregnate the fiber layup. The vacuum draws the bag against the resin/fiber combination and surface of the mold to shape the combination into the desired part. The resin supply lines are typically positioned to introduce resin either at the perimeter of the part such that the vacuum supply line draws the resin across and through the fiber lay up towards the center of the part, or vice versa, with the resin introduced at the center of the part and vacuum drawing the resin towards the perimeter of the part. Vacuum bag molding can usually be categorized as either utilizing, (1) a thin disposable bag made from sheet film, or (2) a reusable bag made from silicone, both of which are flexible bags. Because the resin and fiber are essentially sealed off from the surrounding environment, vacuum bag molding techniques expose tool operators to significantly fewer VOC's than with open molding processes, which is a significant reason why vacuum bag techniques have gained interest in recent years.
When using a disposable vacuum bag, a peel ply release film and a resin flow/bleeder media must often be stacked atop the fiber lay up below the bag because of the nature of the thin sheet film to conform very tightly to the fiber layer up and make resin flow very difficult. The resin flow/bleeder media facilitates flow of the resin across and through the fiber lay up in a timely manner by essentially forming a resin passageway, and the peel ply film ensures that both the media and peel ply layer itself may be easily pulled off of the finished part without undue effort. Additionally, resin and vacuum distribution lines extending from the supply lines and routed beneath the vacuum bag across the mold are often needed in addition to the resin flow/bleeder media to properly distribute the resin and apply the vacuum draw beneath the tightly drawn thin sheet film. Also, adhesive sealant tape is typically applied around the perimeter of the bag to form an airtight seal with the mold and facilitate proper vacuum operation.
Despite the high quality of the part produced using disposable vacuum bag molding techniques (i.e., having a high fiber to resin ratio), certain disadvantages are apparent. For example, many of the aforementioned components used in disposable vacuum bag techniques—including the vacuum bag having resin and vacuum supply lines integrally formed therewith, the resin flow/bleeder media, the peel ply film, the resin and vacuum distribution lines and the adhesive sealant tape—are disposed of after molding only a single part, making this technique prohibitively expensive for all but high margin parts manufacturing. Significant labor is also necessary when using a disposable bag, as the bag must be made by hand to fit the particular base mold and also installed by hand with the resin flow/bleeder media, peel ply film, resin and vacuum distribution lines and sealant tape at the proper positions for the vacuum draw and resin impregnation of the fiber lay up to work Furthermore, if the female mold has a complex shape, many pieces of sheet film may need to be cut and bonded together with sealant tape to produce a bag with the desired shape, thereby significantly increasing manufacturing time per part as compared to open molding processes.
Yet another closed resin transfer molding process involves using rigid male and female molds together to produce fiber reinforced composite parts. A fiber lay-up is placed on the female mold and the male mold is brought into contact with the female mold and clamped or otherwise secured therewith so that a closed space is formed between the molds. Then, a mixed resin and catalyst are injected into the closed space under relatively low pressure. Upon curing of the resin, the molds are separated and the part is removed. The resin transfer molding process is more environmentally friendly than traditional open molding processes, with the capture of any VOC's present in the closed space occurring before the molds are separated to reveal the finished part. One significant disadvantage of resin transfer molding, however, is that because the male and female molds are rigid, if the fiber load of the lay up is not precisely the correct quantity at the correct position, structural weakness in the part occur. For example, “dry spots” occur where the resin cannot flow to an area during the injection process if the fiber density is too high, and if the fiber density is too low, a spot filled with resin and little fiber will develop. Both dry spots and resin filled spots in finished parts are susceptible to fracture or other structural failures at relatively low force loads. These structural weaknesses are even more important when fabricating large parts, such as boat hull components, where the weight of the part itself may facilitate structural failures. Matched, rigid tooling is very expensive to produce and, therefore, the process is less amenable to changes that may be required for structural, process, or styling updates. Rigid tooling molding can result in a higher resin to fiber ratio and weaker parts for a given weight of molded part.
Current closed molding lamination techniques do not provide an economical and reliable solution for fabricating fiber reinforced composite parts, especially with respect to small to medium part runs.
U.S. Pat. No. 6,367,406 discloses a boat and method of manufacturing using a rigid mold, both the male and female halves of the mold are rigid. The boat includes a hull and an internal deck. The internal deck has opposite side chambers containing foam therein. The chambers are formed by a portion of the bottom wall, a floor or top wall and a sidewall extending upwardly from the bottom wall and adjoining the top wall. When the boat is formed, transverse members are formed as an integral part of the structure which can best be seen in FIG. 3. The foam inserts have transverse members that adjoin in the middle which are then covered with fiber which is then infused with resin. The patent specifically requires a seamless construction. The transverse supports extend width wise across the hull and are configured for providing structural reinforcement to the hull. It is specifically required that the support structure, i.e., deck and transverse member forming portions and the hull are preferably formed as a single unitary or monolithic piece such that no seams are discontinuities are located between the two structures. It is also disclosed that there are preferably no separate fasteners or adhesives provided at the connection locations of the various parts of the hull with the connections between the various portions consisting of continuous uninterrupted thicknesses of fiber reinforced plastic material. It is also specifically disclosed that the support structure which includes the transverse supports are simultaneously molded as a single piece within the molding cavity. Further, it is disclosed that the resin is injected under pressure into the mold chamber with the mold members being semi rigid membranes that are capable of at least slightly flexing when pressurized resin is injected into the mold chamber. However, the transverse members formed discontinuities in the walls defining opposite sides of chambers between the deck portions. Stress risers are also provided where there are discontinuities between the fiberglass resin combination and the foam insert. It is believed that this structure, as disclosed, derives the majority of its compressive and tensile strengths from the fiber/resin laminate necessitating thicker and heavier laminates with concentrated stresses in places where the laminates are not continuous.
The present invention overcomes these difficulties by providing a one step or one shot molding process to form a relatively complete boat hull with the various interior portions of the boat hull, for example, the working deck, formed as a monolithic and integral structure with substantially seamless component joiner of certain of the major components. The molding process also permits easy formation of desired seams at desired locations with simple tooling during a single step molding process. The boat hull and working deck form the major portion of the finished boat or boat precursor. One or more partitions may be easily added between working deck components after forming the hull and working deck.